Mn–Fe/ZSM5 as a low-temperature SCR catalyst to remove NOx from diesel engine exhaust

Abstract A Mn–Fe/ZSM5 catalyst has been developed for removing NOx from diesel engine exhausts and its excellent low-temperature SCR activity and N 2 selectivity demonstrated in comparison with other representative SCR catalysts including CuZSM5 and a Cu-based commercial catalyst (COM). The well-dispersed MnO 2 and the high NH 3 adsorption capacity of the Mn–Fe/ZSM5 catalyst have been identified as the primary sources for its high deNOx activity for NH 3 /SCR. Hydrothermal stability and durability of the Mn–Fe/ZSM5 catalyst have been examined and compared to those of the CuZSM5 and COM catalysts. The hydrothermal stability of the catalyst improved upon the increase of Mn content and/or the addition of Er, the latter of which helps to stabilize the dispersion of MnOx on the catalyst surface during hydrothermal aging. The deNOx activity of the Mn–Fe/ZSM5 and its Er-promoted counterpart was less affected by HC poisoning, C 3 H 6 poisoning in particular, compared to the CuZSM5 and COM catalysts, mainly due to the excellent C 3 H 6 oxidation activity of MnO 2 . No poisoning of the Mn-based ZSM5 and CuZSM5 catalysts has been observed upon the addition of 2 wt.% of K + and Ca 2+ to their surface, primarily due to the high NH 3 adsorption capacity of the ZSM5 support, whereas the COM catalyst has been severely deactivated by the deposition of K + and Ca 2+ . The deNOx activity of the Mn-based ZSM5 catalyst, particularly the Er-promoted one, was less affected by SO 2 compared to the CuZSM5 and COM catalysts, although it was hardly regenerated at 500 °C. Formation of MnSO 4 on the catalytic surface appears to be the primary cause for the deactivation of the Mn-based ZSM5 catalysts in the presence of SO 2 in the feed gas stream.